EF7 Migrations - The corresponding CLR type for entity type '' is not instantiable

I'm trying to use EF7 migrations and got stuck when I modeled an Organization model with inheritance.

Organization is an abstract class. There are two concrete classes that inherit from it called Individual and Company.

I set the Organization abstract class as DbSet<Organization> in DbContext and run migrations.

I'm following this tutorial here.

The following error is shown:

The corresponding CLR type for entity type 'Organization' is not instantiable and there is no derived entity type in the model that corresponds to a concrete CLR type.

Whats should I do?

public abstract class Organization
{
    public Organization()
    {
        ChildOrganizations = new HashSet<Organization>();
    }

    [Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int Id { get; set; }
    public bool Enabled { get; set; }
    public bool PaymentNode { get; set; }
    public DateTime Created { get; set; }
    public DateTime Updated { get; set; }

    // virtual
    public virtual ICollection<Organization> ChildOrganizations { get; set; }
}

public class Individual : Organization
{
    public string SocialSecurityNumber { get; set; }
    public string Firstname { get; set; }
    public string Lastname { get; set; }
}

public class Company : Organization
{
    public string Name { get; set; }
    public string OrganizationNumber { get; set; }
}

public class CoreDbContext : IdentityDbContext<ApplicationUser>
{
    public DbSet<Organization> Organization { get; set; }

    public CoreDbContext(DbContextOptions<CoreDbContext> options)
        : base(options)
    {
    }

    protected override void OnModelCreating(ModelBuilder builder)
    {
        base.OnModelCreating(builder);
        // Customize the ASP.NET Identity model and override the defaults if needed.
        // For example, you can rename the ASP.NET Identity table names and more.
        // Add your customizations after calling base.OnModelCreating(builder);
    }
}

Thanks in advance!